Irrigation Water Management
(IWM)
Bill Cronin, P.E.
What Is Irrigation Water Management?
• When do I apply Irrigation Water?
• How much water do I apply?
• How fast do I apply the water?
Applying the right amount
of water at the right time.
Why All The Attention on Irrigation Water
Management?
USA FRESH WATER USE
Domestic, Livestock,
Aquaculture, Mining
OREGON FRESH WATER USE
Domestic, Livestock,
Mining, Power Generation
unicipa
l
8%
Public-M
%
Industrial 3
icipal
11%
Public
, M un
5%
Indu
stria
l
2%
1%
Irrigated Agriculture
Steam Powered
Electrical Generation
34%
48%
Irrigated Agriculture
88%
Source=http://water.usgs.gov/pubs/circ/2004/circ1268/htdocs/table04.html
Why Should I Use Irrigation Water
Management Scheduling?
• Maximize plant health and production
• Over watering a crop can become very expensive. Electrical
pump costs, fertilizer costs, and labor costs will be higher.
Under and over watering can damage crop yields
• Environmental impacts are minimized when the correct amount
of water is applied. Helps keep operations within regulatory
limits. Limits runoff, deep percolation.
• IWM is necessary for designing irrigation systems and
correctly operating them.
• Conserve water and maximize profits.
IWM TERMS TO KNOW
When Should I Irrigate, or How Often? = Irrigation
How Much Water Should I Apply? = Set
Interval (days)
Time (hours)
How Fast Should I Apply the Water? = Type
of Irrigation System
(Nozzle size, etc,) (inches/hour)
Crop Yield (Tons/Acre)
Crop Yield Versus Applied Irrigation
Under Irrigation
Optimal
Applied Irrigation (Gross Inches)
Over Irrigation
What Do I Need to Perform IWM Scheduling?
• Soil Information
• Crop Information
• Climate Information
Crop water use
• Skills and Desire
Evapotranspiration (ET)
• E = Evaporation from
plant and soil
surfaces
• T = Transpiration from
plant canopies
ET = E + T = Crop Water Use
Plant
Transpiration
As a leafs guard cells shrink, stomata open and water is lost to the
atmosphere through evaporation.
Transpiration is Responsible for:
• Transporting soil minerals and nutrients throughout the plant
• Cooling the plant through evaporation
• Moving sugars and plant chemicals (for photosynthesis)
• Maintaining turgor pressure (keep plants hydrated).
Factors Influencing
Evapotranspiration
 Temperature
 Humidity
 Wind
 Sun Exposure
 Available Soil Moisture
Plant Types
Irrigation Types
Effective Rooting Depth
“Depths to which the roots of mature crops will extract
available soil water from a deep, uniform, well drained
soil under unrestricted conditions” 80% of the maximum
root depth.
Effective Root Depth = Depth of Managed Soil Water Reservoir
Crop
Effective Root Depth (ft)
Alfalfa
5
Pasture Grass
2-3
Cranberries
0.5
Grapes
5
Fruit Trees
4-5
Grass Seed
3-4
Onions
1-2
Source = NRCS National Engineering Handbook Part 652, Table 3-4
http://www.wcc.nrcs.usda.gov/nrcsirrig/irrig-handbooks-part652.html
Soil-water basics
Soil
Particles
Gravitational
Water
Available
Water
Unavailable
Water
Soil Water Unavailable
To Plants
Oven Dry
MAD
Water Available
To Plants
Under Stress
Permanent Wilting Point
Soil Water Managed
by Irrigation Scheduling.
Minimum Allowed
Field Capacity
Saturation
Readily
Drained Water
Soil Water Reservoir Definitions
Deficit Irrigation
A pp
ly Irr
igati
o
n
Apply
Irrigatio
n
Apply Irrigation
Soil Water Content (in)
Field Capacity
Irrigation Interval
Management Allowed Depletion (MAD)
Time (days)
Crop
Alfalfa
Management Allowed
Depletion (%)
50
Pasture Grass
50
Cranberries
30?
Potatoes
35
Fruit Trees
50
Grass Seed
50
Onions
35
Available Soil Water
Available Water (in/ft)
3
2.4
2.5
1.9
2
1.6
1.5
1
0.5
0.25
0
Clean Sand
Sandy Loam
Clay
Silt Loam
What Makes a Good Agricultural
Soil?
A mixture of sand, silt, clay and organic matter,(Loam)
How Do I Estimate the Soil Water
Content and Schedule Irrigation?
• Directly by Touch and Feel
• Indirectly by many types of soil moisture
sensors.
• Use real time Agrimet ET data and the
checkbook method.
• Use typical year historical average ET data
Appearance and Feel
Advantages
1. Soil auger is the only
tool needed
2. No expensive tools or
data loggers needed.
Disadvantages
1. Accuracy is marginal
2. Experience required!!
3. Labor requirements
may be restrictive.
http://www.mt.nrcs.usda.gov/technical/ecs/agronomy/soilmoisture/index.html
Many Soil Moisture Sensor Choices
Check Book Method of Irrigation Scheduling
• Water deposits are rain and irrigation.
• Water withdrawal is through ET.
• You must keep a minimum soil water balance or
you pay penalties through reduced production.
Typical Year IWM Scheduling Spreadsheet
NRCS IRRIGATION WATER MANAGEMENT SHEET
Land Owner, Location, and Field Information
Climate Site Information
Landowner:
County:
Legal Description:
Climate Site:
Jackson
MEDFORD AIRPORT
Tract #:
Designer/Assistance Information
Field #:
County:
Jackson
Acres Irrigated:
Assisted By:
1
Soils Information
Soil Map Symbol
Soil Name
Soil Profile Managed (in):
Max. Soil Water Deficiency (%):
Maximum Application Rate (in/hr):
Soil water at Field Capacity (in):
Average total Soil Depth (in):
Soil Surface Slope (%)
Crop Information
31A
Crop:
CENTRAL POINT
PASTURE GRASS
Maximum Rooting Depth (in):
24
24
Effective rooting depth (in):
50
0.40
2.40
67
24
Annual Net Water Requirement (in):
Annual Gross Water Requirement (in):
Annnual Water Requirement (acre-ft):
24.91
36
3.0
Maximum Daily ET (in/day):
0.26
0 to 5
IWM Design Information Based on Peak Crop Water Demand
Water Availability:
WEC
Date:
System Operating Parameters
On Demand
# of Days to Complete 1 Irrigation:
5
Application Efficiency (%):
70
Hours/day of Operation:
18
Conveyance Efficiency (%)
100
Area Irrigated/Day (acres/day):
0.2
Combined (project) efficiency (%)
Net Irrigation Application (in)
Gross Irrigation Application (in)
Design Irrigation Interval (days):
70
1.21
1.73
5
# Days to Irrigate Acreage:
Actual Application Rate (in/hr):
5
0.3
Design Set Time (hours):
5.8
Water Right (gpm):
Peak Design Flow Rate (gpm)
8.7
80% of Design Flow Rate (gpm)
Water Right Information
9
7
Irrigation Scheduling Information
Month
Net Monthly Irrigation Requirement (in)
Average Irrigation Interval (days)
Average # of Irrigations
MAR
0.00
0.04
0
0
APR
0.80
Average Daily ET (in/day)
0.08
30
1
MAY
3.08
0.12
10
3
JUN
4.97
0.18
8
4
JUL
6.59
0.22
6
5
AUG
5.73
0.20
6
5
SEP
3.43
0.13
10
3
OCT
0.31
0.07
0
0
NOV
0.00
0.05
0
View Graph
View Graph
View Graph
0
View Graph
• Based on historical climate and ET data
• Uses historical averages (Median) to calculate irrigation scheduling
• Contact your local NRCS-SWCD office for assistance.
Average Daily ET (in/day)
RESULTS IWM SPREADSHEET
0.25
0.20
0.15
0.10
0.05
0.00
MAR
APR
MAY
JUN
JUL
AUG
SEP
OCT
NOV
SEP
OCT
NOV
SEP
OCT
NOV
Average Irrigation Interval (days)
35
30
25
20
15
10
5
0
MAR
APR
MAY
JUN
JUL
AUG
Average # of Irrigations
6
5
4
3
2
1
0
MAR
APR
MAY
JUN
JUL
AUG
Climate Site = Medford Airport
Crop= Pasture Grass/Hay
Soil = 31A, Central Point Loam
Depth of soil managed = 2 ft
When's the best time to run an irrigation
system based on water conservation?
When the Temperature is low
The relative humidity is high
Little or no wind
Ross Lane Field Visit Site
Evans, Medford Soils
Evans Loam
55A
3.5" Water
in top 20" soil
Medford Silty
Clay Loam
127A
3.3" Water
in top 20" soil
Taylor Road Field Visit Site
Barron coarse sandy
loam 10B
2" water in top 20" soil
Kubli Loam 100A
3.4" in top 20" soil
Central Point, Kubli, Barron
Loam soils
Central Point Sandy Loam 31A
2" water in top 20" soi;
QUESTIONS?